As an example of existing prior art, in nail guns in which compressed air is used as a driving force, a driving operation is configured to be performed by a main body. This operation is performed on the conditions that a contact arm provided at a tip end of a nose part of the body for driving is moved upwards with respect to an injection opening, that the contact arm is pushed toward a material to be driven (an on-operation of the contact arm), and that a trigger is pulled by a fingertip (an on-operation of the trigger). The driving operation is configured so as not to be performed by only one of the above on-operations, thereby preventing an inadvertent driving operation where all conditions are not met.
Furthermore, in these conventional types of driving tools, various driving operations can be performed, such as a focused driving operation in which the trigger is pulled after the contact arm is on-operated by pushing the contact arm toward the material to be driven, a dragged driving operation in which the trigger is on-operated while the driving tool is moved with the contact arm being on-operated, and a swung driving operation in which the contact arm is turned on/off by moving the driving tool in an up-and-down direction while the trigger is being pulled. In the focused driving and the dragged driving operations, unless the trigger is turned off after the driving operation is performed, the next driving operation cannot be performed (a single driving mode). On the other hand, in the swung driving operation, a continuous driving can be performed while the trigger is being pulled (a continuous driving mode). Japanese Laid-Open Patent Publication No. H9-109058 discloses a mode switch technique in which the single driving and the continuous driving modes can be switched from one mode to the other based on which of the on-operations, of the contact arm or of the trigger, is performed first (a sequential control).
Furthermore, Japanese Patent No. 3287172 discloses a mode switch technique in which each of the on-operations, of the contact arm and the trigger, is respectively detected by a micro switch and an elapsed time after the on-operation of the trigger is measured by a timer. According to this switch technique, in the single driving mode, a driving operation is performed by the on-operation of the contact arm before a predetermined time has passed after the trigger is on-operated. After that, the driving operation is forbidden. This forbidden state can be reset by turning off the trigger.
In contrast, in the continuous driving mode, the reset of the timer and the driving operation can be repeatedly performed on the condition that the contact arm is on-operated before a predetermined time passes after the on-operation of the trigger. At the point in time when the contact arm is not on-operated within a predetermined time measured by the timer, an on-operation after that time is invalid and subsequent driving operation is forbidden. Alternatively, the driving operation can also be forbidden by engaging the contact arm with a lock pin in order to lock to an off position. According to this mode switch technique, for example, in the continuous mode with a grip being held and the trigger being on-operated, even when the contact arm contacts any other portion by accident while the main body is carried, an inadvertent driving operation can be prevented.
However, according to the technique disclosed in Japanese Patent No. 3287172, in a case where a remaining capacity of a battery has decreased and simultaneous power is not being supplied to a controller etc. that can be operated by input signals from the micro-switch or other devices, or in a case where power supply is shut off, the driving operation cannot be performed at all and eventually a work has to be stopped.
The present invention was conceived in order to overcome this known problem, and an object of the present invention is to continue performing the driving operation even if the remaining capacity of the battery becomes low etc.